1. Field of the Invention
The present invention relates to a semiconductor device suitable for use in a static induction thyristor, a GTO thyristor, etc., and to a method for producing the same. More specifically, the present invention relates to a semiconductor device containing an active high-resistance semiconductor layer (active intrinsic layer AIL), which exhibits high resistance and is effective at shortening the carrier lifetime, as well as to a method for producing the same.
2. Description of the Related Art
Static induction thyristors and static induction transistors have been developed and used practically as power semiconductor devices. For improving speed, lifetime control of such semiconductor devices has been carried out using electron beam irradiation, heavy metal doping, or the like. In general, in a case where a high-resistance semiconductor layer is not doped with an impurity, since crystalline perfection of the layer is increased, the lifetime is lengthened. Therefore, in this case, in a semiconductor device having a high-resistance semiconductor layer such as a static induction thyristor or a static induction transistor, advantageously, properties of the device can easily be controlled by selecting the device structure, and an original function based on the device structure can be obtained.
In the event that the high-resistance semiconductor layer is doped with an impurity, due to different lattice constants between the impurity atoms and the layer, the crystal is likely to become strained, thereby causing dislocations such as a misfit dislocation.
Lattice strains caused in vapor-phase growth of Si (silicon) due to an impurity concentration difference between a semiconductor substrate and a growth layer have been studied by Nishizawa et al. (see, J. Nishizawa, T. Terasaki, K. Yagi, and N. Miyamoto, “Perfect Crystal Growth of Silicon by Vapor Phase Epitaxy,” J. Electrochemical Society, Vol. 122, No. 5, P. 664-669, 1975).
In a single Si crystal, the Si atoms are regularly arranged. In the case that the Si crystal is doped with an impurity, the Si atoms are replaced by impurity atoms, and since the impurity atoms are atoms having a covalent radius smaller than that of the Si atoms (such as boron (B) or phosphorus (P) atoms), the distance between the impurity atoms and the adjacent Si atoms is smaller than the distance between the Si atoms alone. Therefore, when a high concentration of B or P impurity atoms are added to a Si crystal, the doped Si crystal exhibits a lattice constant smaller than that of an intrinsic Si crystal. On the other hand, in the case that the impurity atoms are atoms having a covalent radius larger than that of the Si atoms (such as arsenic (As) or antimony (Sb) atoms), an opposite result is obtained (see, L. Pauling, “The Nature of Chemical Bonding,” Cornell University Press, 1960, p. 205).
A semiconductor device having an active high-resistance layer (AIL) and a method for producing the same, which involves disposing p-type and n-type impurities at high concentrations in approximately the same positions to shorten the carrier lifetime, have been proposed. Such an active high-resistance layer can have a substantially high resistance, and can exhibit a shortened carrier lifetime due to the compensating effect of the p-type and n-type impurities. For example, when the semiconductor device is used as a diode, a transistor, a thyristor, an insulated gate device, or the like, a high switching speed, low loss, and low ON-resistance can be achieved (see, Japanese Laid-Open Patent Publication No. 2005-285955).